Various methods have been proposed to provide address information in an optical disk substrate and optical disk, and in order to meet demands for high-density recording, a method for allowing a tracking-use groove itself to have address information has been proposed. More specifically, in the method, the tracking-use groove is provided in a winding fashion and the address information is found by extracting a winding frequency component from the tracking signal.
Moreover, as illustrated in FIGS. 23(a) through 23(c), Japanese Laid-Open Patent Publication No. 314538/1993 (Tokukaihei No. 5-314538) discloses a method wherein: in an optical disk substrate, only one of the side walls of a groove is allowed to wind in accordance with address information, and only the one side is subjected to a reading operation by using a recording-reproduction-use light spot 4 whose diameter is smaller than double the groove width, so as to find the address information. FIG. 23(a) is an explanatory drawing that shows a manufacturing method of this optical disk substrate, FIG. 23(b) is an explanatory drawing that shows how to read information from an optical disk using the optical disk substrate of this type, and FIG. 23(c) is a cross-sectional view of FIGS. 23(a) and 23(b).
However, in the optical disk substrate that is shown in FIG. 23, during its manufacturing process, at least two laser light beams 30a and 30b are applied in the radial direction in a spaced relationship with one another, while only one of the laser light beams is oscillated in the radial direction in accordance with the address information during the application. More specifically, the laser light beams 30a and 30b are applied in a manner so as to respectively follow lines 30c and 30d in FIG. 23(a). Since the laser light beam is split into two, the resulting problems are that the efficiency of light utilization is decreased, that a complex optical system is required, and that the respective laser beams have to be controlled individually.